Work is in progress to develop procedures for long-term preservation by freezing of transplantable organs which require perfusion by blood for resuscitation and prolonged survival following reimplantation. A programmed thermally controlled liquid perfusion system that has the capacity to control a number of parameters, including perfusate composition, flow, pressure, cycling, oxygenation, sterility, and temperature is being employed. A systematic comparative evaluation of the cryophylactic properties of a number of newly synthesized agents are to be investigated. Preliminary studies will be conducted using canine lymphocytes and activated mouse spleen cells in a cellular assay system. Transplanted fetal mouse hearts will constitute an organ model assay system. Data derived from these procedures hopefully can be extrapolated to improve survival rate of larger cryopreserved mammalian organs in subsequent studies. Studies will be performed with rabbit kidneys to establish optimum thawing conditions using a microwave unit.